This invention relates to fluids having recyclable viscosity and their use in oilfield treatments. More particularly, it relates to compositions and methods for cleaning debris from wellbores and wellbore tubing. Even more particularly it relates to removal of drill cuttings and other contaminants from a wellbore before or after cementing or completion and to removal of particulates after stimulation and/or during production. Most particularly, it relates to methods and compositions for recycling a fluid used in such cleanout operations.
Material that has accumulated in a wellbore before or during completion is often called wellbore fill; it may be sand, proppant, cement chunks, or other materials. Such materials hinder or prevent operations. Sand accumulated in production tubing in a wellbore at the start of or during production can greatly hinder production. Coiled tubing has been widely used as a means to clean out the wellbore or production tubing in these situations. Requirements for fluids used for wellbore fill removal, more particularly “coiled tubing cleanout”, include low friction pressure and good particle carrying capability. Some crosslinked polymer gels are not preferred viscosifiers for cleanout fluids because they do not have preferred viscoelastic properties for fluidizing the particles so that they can be transported. Viscoelastic Surfactant (VES) fluid systems have been successfully applied in coiled tubing cleanout applications because of their superior drag reduction and particle transport properties, but these materials are discarded after a single trip through the well. VES cleanout systems that can be recycled have not been reported, and would be highly desirable for logistical and operational reasons, especially in offshore locations. Such recyclable VES cleanout systems also give cost benefits and are environmentally friendly.